Documents a constraint between two DynamicColors, in which their tones must
have a certain distance from each other. Prefer a DynamicColor with a
background, this is for special cases when designers want tonal distance,
literally contrast, between two colors that don't have a background /
foreground relationship or a contrast guarantee.
Describes the different in tone between colors. If there is no preference,
the tones at standard contrast are examined and the polarity of those is
attempted to be maintained.